ae 
194 Mr Potts, The Swarming of Odontosyllis. 
direction, rid itself of its contents as quickly as might be, and then 
lost no time in descending to its accustomed habitat. The pheno- 
menon continued till the light had nearly faded, but by then there | 
were only very occasional individuals to be seen, so that probably — 
the whole period of swarming is less than an hour. 
On the following day I left Nanaimo, but I was afterwards told - 
that, though a few individuals were seen on the surface on that — 
night and the next, there were nothing like the numbers of the — 
two preceding nights. : 
The accompanying map shows the distribution of O. phosphorea | 
in the neighbourhood of Nanaimo. In explanation of the small 
area assigned to the swarming worms, it must be noticed that the | 
short time did not allow a complete investigation of their distribu- | 
tion, but doubtless future observers will be able to map out the | 
area more completely. One fact is quite clear; that the worms, 
in seeking the surface, migrate inshore in considerable numbers, | 
for I never, in the course of many dredgings, found a single 
example of Odontosyllis in Departure Bay itself. 
Recently Professor McMurrich has been kind enough to send 
me very interesting information which establishes the periodic 
appearance of the swarms of Odontosyllis. ‘The weather was very | 
unfavourable in 1912 and there had been a great deal of rain just | 
before August 18th. On that night, however, the weather was | 
fine, and on going out at 7.30 p.m. Professor McMurrich found 
Odontosyllis swarming at the surface as in the year before. | 
Dr Fraser again observed the phenomenon on the two or three 
evenings following. 
It seems certain, then, that the swarming of Odontosyllis | 
phosphorea takes place at Nanaimo at approximately the same 
date every year. In 1912 it occurred three days later than in 
1911, but this may possibly have been due to the unfavourable | 
weather. In 1911 swarming took place during the last quarter | 
of the moon and in 1912 at the beginning of the first quarter. In 
both cases the tide was full or just falling. The close proximity | 
of the Dominion Government Biological Station will allow of a close 
watch being kept on the circumstances of the appearance from | 
year to year, and I trust that the scanty data which I give here | 
will soon be supplemented. In particular I hope that enquiry | 
will be made as to whether swarming takes place at any other | 
period of the year*. i 
For some time I supposed that the phenomenon witnessed at 
Nanaimo had not been previously described in Odontosyllis, and it | 
* In the original description by Moore (loc. cit.) he states that the type 
specimens were labelled ‘‘Phosphorescent annelids caught at surface; Avalon | 
Bay, Catalina Island, evening, April 11, 1904.” This fixes a date for the swarming | 
of this species in California. 
) 
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